Large caverns are solution-mined in salt formations and subsequently used for the storage of hydrocarbons such as petroleum and petroleum products. Caverns in salt domes, usually known as wells or jugs, are routinely used for storing high vapor pressure, low molecular weight hydrocarbons such as ethane, ethylene, propane, propylene, and butane. The hydrocarbon is stored on top of brine in the well. When the hydrocarbon is transferred to the cavern, brine is displaced to an open pit. Brine is subsequently pumped from the pit into the well to displace and thereby recover the hydrocarbon.
Salt formations which are solution-mined to form caverns often contain large quantities of gases such as methane and ethane as well as carbon dioxide. When liberated by the dissolution of the salt, these gases dissolve in the brine. Further, when fresh waters from open reservoirs and streams are used to solution mine the salt, oxygen and nitrogen from the air dissolved in the fresh water are carried into the caverns and remain dissolved in the brine. Such contaminating gases (O.sub.2, CO.sub.2, CH.sub.4, C.sub.2 H.sub.6, etc.) are many times more soluble in stored liquid hydrocarbons such as ethylene, propylene, propane, etc., at well storage conditions than in brine. Thus, with long exposure times, large quantities of the gases in the brine are transferred to the stored hydrocarbon. Often the quantity of gases transferred is sufficient to exceed specifications for contaminating gases in the stored hydrocarbon. Reprocessing of the stored hydrocarbon is sometimes required to reduce the contaminating gases below specified amounts.
A process for removing contaminating gases from water in an underground cavern is disclosed in U.S. Pat. No. 3,289,416. The disclosed invention requires heating the water and stripping the heated water in a simple tower with a suitable stripping gas to remove the CO.sub.2 and O.sub.2 which normally would be liberated at that temperature and a portion of the remaining dissolved CO.sub.2 and O.sub.2, depending upon the efficiency of the column. This process, however, is relatively inefficient compared to the present invention, as explained hereinafter.
Other patents considered pertinent to the present invention include U.S. Pat. Nos. 3,083,537; 2,104,759; and 3,856,482.